Nicholas Berg came to Iraq in December with little more than a bag of tools and a desire to find work in his chosen trade: repairing transmission towers. He hoped to tap the opportunities available to individual contractors willing to brave the hazards of living in a war-scarred country.

In the four months before he was decapitated by Islamic guerrillas who said they were avenging the mistreatment of Iraqi prisoners by U.S. soldiers, Berg was robbed once, detained twice and held for 13 days by Iraqi police who were both incredulous and suspicious that an American would travel alone.

Yet he resisted the advice of friends and family members to leave Iraq, despite the emergence in early April of a violent insurgency and the frequent abductions and killings of foreigners, irrespective of nationality or occupation.

"The good thing was that he meant no harm to anyone," said Radhi Munthri, an Iraqi who worked for Berg as a driver. "The bad thing was that he never listened to anyone."

The portrait of Berg that emerges from interviews with his associates here and his family in Pennsylvania, as well as from his e-mails to friends, depicts an independent, optimistic and somewhat reckless young man who impressed engineers with his technical knowledge but exasperated others with his naive willingness to take risks.

His carefree nature may have contributed to his untimely death. A video distributed on the Internet on Tuesday showed five masked, black-clad gunmen beheading Berg and attributed the act to Abu Musab Zarqawi, a Jordanian militant who is wanted by the United States for the killing of a U.S. official in 2002. The CIA said Thursday that it believed Zarqawi was behind the killing of Berg.

Nicholas Evan Berg graduated from high school in 1996. The former Boy Scout studied engineering at Cornell University but dropped out and later took a job working in Texas for a company that built radio towers. He traveled in Africa and started his own business, Prometheus Methods Tower Service, in his home town of West Chester, Pa., outside Philadelphia.

Unafraid of heights or travel, Berg became excited by the idea of going to Iraq to help repair radio and television towers that had been damaged during the war last year. In early December, he and 400 other people attended a two-day conference at a hotel in Arlington promoting opportunities to rebuild Iraq.

"He was clean-cut, well educated," said Richard Greene Jr., who met Berg at the conference and stayed in touch with him by e-mail. "He came across as a professional."

Berg became convinced that the only way to find work in Iraq was simply to go, according to Greene, who owns a small technology company in Fayetteville, N.C., that employs eight people in Iraq through a subcontract with the U.S. government.

"In order to get a contract on the ground there, you need to be in-country," Greene said. "You need to have a presence. Nick decided to go over and see if he could find some work."

Fearful of the dangers, Berg's mother implored her son to change his mind. She even worried that his favorite blue-checked shirt would make him stand out as a foreigner. "We definitely did not want him to go," Suzanne Berg said in a telephone interview.

Berg left the United States in December, flying to Tel Aviv and then to Amman, Jordan, before getting a ride to Baghdad. He checked into the large Babylon Hotel, in the well-to-do Jadriyah neighborhood, and began making business proposals to various companies working on reconstruction projects.

Omar Abdul-Karim, who met Berg in January, said he used to pick up an American colleague from the same hotel and was startled to see Berg take a taxicab to the Green Zone, the heavily fortified compound that serves as the headquarters of the Coalition Provisional Authority.

"He was careless," said Abdul-Karim, an Iraqi operations manager for ASCS/GSCS, a construction and services company based in Abu Dhabi, in the United Arab Emirates. "We told him so many times: You should not go anywhere without security. He was not listening to this."

One of the people Berg met in Baghdad was Aziz Taee, an Iraqi who studied electrical engineering at Temple University and has lived in the Philadelphia area for most of the past 20 years. Taee is chairman of the Iraqi American Council, a business group based in Annandale that encourages investment in Iraq.

Berg had visited the group's Web site and communicated with Taee by e-mail. When the two men finally met, Taee was impressed enough that he agreed to start a small company with Berg, called Shirikat Abraj Babil, or Babylon Towers Co.

They printed business cards advertising their services in installing, inspecting and repairing telecommunications and utility towers. They rented a small corner office on the second floor of a building in Jamiaa, a neighborhood in western Baghdad.

Taee, 40, said he sometimes worried about his 26-year-old associate, who would wander freely around Baghdad.

"He had a short haircut, like the Marines, and he was well built," Taee said. "Most people thought that he was an Army guy in civilian clothes. He took a lot of risks. He was a guy who loved adventure and risk."

Wearing a large tool belt and using metal grippers and rope, Berg began climbing transmission towers, taking photographs of structural damage that he would later show to prospective clients. The work, which was itself dangerous, took him to hostile areas.

Once, he climbed a tower in Abu Ghraib, an impoverished western suburb of Baghdad infamous as the site of Iraq's largest prison. A local farmer became enraged, thinking that Berg was trying to steal parts of the already damaged structure.

Another time, Berg was briefly detained in the southern city of Diwaniyah by Iraqi police who became suspicious when they noticed an American traveling alone. Berg also was robbed one night in Baghdad near his hotel, Taee said.

Without having found steady work, Berg returned to the United States in February and stayed for about a month. Then he caught a flight from New York to Amman on March 14.

His business prospects had improved. He now hoped to get work helping to build and repair radio and television towers for the Iraqi Media Network, a U.S.-funded organization that is intended to become the country's public broadcasting service. The network, which broadcasts under the channel name al-Iraqiya, had hired a primary contractor and two subcontractors to carry out the work.

Berg met with representatives of Al-Fawares, one of the subcontractors, and showed them his photographs. They were impressed by his level of knowledge. "We nicknamed him 'Nick the Tower Man' because he was familiar with all the towers," said Amer Mardam-Bey, an American project manager for Al-Fawares. "He was a unique individual, in the sense that he appeared to live for climbing towers and knew anything and everything having to deal with towers."

Berg arranged to call Mardam-Bey after he returned from a trip to the northern Iraqi city of Mosul to visit a distant relative. At 6:30 p.m. on March 23, he checked into Room 102 at the $25-a-night Al-Kalaa Hotel, in Mosul's southern Guzlani district.

"He seemed very nice and extremely friendly," said Khalid Mahmoud, a clerk at the hotel. "There was nothing unusual about him." Mahmoud recalled being surprised, however, that Berg had Iranian and Jordanian currency in his pocket, along with Iraqi dinars.

At 10 a.m. the next day, Mahmoud said, Berg left the hotel, saying he was going to visit friends in the eastern part of the city. He never returned. In his room, the staff later found an Arabic-English dictionary and a book in Persian.

Around 9 p.m., Berg was detained near the hotel by Iraqi police. "He seemed confused, and he was taken in by the police patrol," said 1st Lt. Sayel Abdullah, the officer in charge of the Guzlani district.

The police, who placed Berg in the central jail in Mosul, notified a local U.S. military police commander. "We were informed of this man being picked up by the Iraqi police, so we made sure that he got food to eat and a cot to sleep on," Army Lt. Col. Joseph Piek, a military spokesman in Mosul, said Thursday.

The military informed the FBI, which sent agents to interview Berg on March 25 and 26. The substance of the interviews is still not clear, but after a third interview about a week later, the FBI determined that he was not suspicious.

In the meantime, Berg's parents had prepared a petition for the U.S. District Court in Philadelphia, arguing that the U.S. military had illegally detained their son despite an FBI recommendation that he be released. They contended that his detention prevented his planned return to the United States on March 30.

The petition was filed April 5, and Berg was freed the next day. It is not known why he was held for 13 days.

Berg returned to Baghdad and the Al-Fanar, a hotel popular among foreigners, including freelance journalists and independent businessmen. He had stayed at the eight-story hotel, on the east bank of the Tigris River, the night before he left for Mosul.

He told one guest, Hugo Infante, a Chilean journalist, that he was arrested only because he had an Israeli stamp in his passport. Berg was Jewish.

Infante was impressed by Berg's cheerfulness. "He never said a bad word about the country," he said. "He loved the Iraqi people."

Andrew Robert Duke, an American business consultant who lived two doors down from Berg on the sixth floor, said that Berg shrugged off his detention as "a minor inconvenience."

On April 8, Berg sent Taee an e-mail explaining why he hadn't been in touch. "I realize you must think I am a real flake for not contacting you as promised, following the last time we spoke in Baghdad," Berg wrote. "Suffice it to say I ran into a little problem in Mosul which held me there for the last two weeks."

The most violent month since the start of the war had begun, and the e-mail betrayed some anxiety: "If you are still in Baghdad, I hope you're keeping your head down. It's getting tough around here. Take it easy and stay in touch!"

On April 10, Berg left the Al-Fanar, leaving behind several belongings -- books, weights and a business-card wallet. In the next three weeks, the State Department sent a consultant to the hotel with Berg's photograph, his frantic family hired a private investigator to help locate him, and Taee even pulled up the records on his Iraqi cell phone to track down leads. Nothing worked.

On Saturday, soldiers on patrol found Berg's body hanging from a highway overpass in Baghdad. His family was notified on Monday. They held a private funeral service on Thursday.

"This is the part that really tears at me: He was really looking forward to having a life, having a relationship with a woman, having children," Duke said. "He was looking forward to that: the pleasure of Thanksgiving, the pleasure of Passover."

Special correspondent Khalid Saffar in Mosul and staff writer Ariana Eunjung Cha in Washington contributed to this report.

Nicholas Berg Nicholas Berg is shown with his company banner at a conference in Hershey, Pa. He started the firm after working for a company that built radio towers.The CIA says that it believes Abu Musab Zarqawi, a native of Jordan, was behind the beheading of Berg.