An empty envelope that once held cash, an unexplained fresh wound and a shaky alibi helped lead to the arrest of Mark K. Makki on Sunday night in the strangling of his mother at their Potomac home, a police charging document says.

The 23-year-old man was charged with first-degree murder and robbery in the homicide of Shohreh Seyed-Makki, 54.

A family friend, who was asked to check on Seyed-Makki on Thursday evening, found her body on the kitchen floor of the family's home, in the 9500 block of Newbridge Drive.

Montgomery County detectives initially cast a wide net in the investigation. But they soon zoomed in on the youngest member of the Makki family.

A charging document written by Montgomery police officer Gary F. Turner provides the following account of events:

Khosrow S. Makki, 53, the victim's husband, and Amanda Makki, 27, their daughter, told detectives that Mark Makki and his mother fought often because she did not approve of his girlfriend, Aramis Mizani.

Mark Makki told detectives that his mother "frequently confronted him about their relationship and has attempted in the past to break up their relationship," Turner wrote.

The suspect also told them that he had been at his girlfriend's house the day his mother was killed and that he learned of her death Thursday evening when he returned to the family home.

He told investigators that "his girlfriend could provide an alibi as to his whereabouts," the charging document said.

Makki told police that he and Mizani went to a Montgomery College library Thursday and also spent time at her house. In addition, he told them that several months ago, he discovered a place in his family's house where his mother kept money and valuables.

Police say that when detectives interviewed Mizani at police headquarters Thursday night, Makki's story began to disintegrate.

She told police that her boyfriend had picked her up at the airport Wednesday after she flew in from Florida. The couple drove to her home, but Makki did not spend the night with her, Mizani told detectives. Makki told Mizani that he was going home, she added.

Makki returned to her home late Thursday morning, and they spent the afternoon together, she told police.

"When asked if the defendant went to the library at Montgomery College, Mizani stated that the defendant did not," Turner wrote.

Investigators confronted Makki with the discrepancies between his story and his girlfriend's statements.

"It was at that time the defendant admitted that he lied to detectives about visiting the library," Turner wrote. "When asked if he stayed at his girlfriend's home [Wednesday night] he professed that he had.''

Mizani could not be reached for comment yesterday.

Detectives said that Mark Makki had a "fresh, superficial cut," whose cause he could not explain.

Police obtained a search warrant to collect his belongings. When officers gathered Makki's clothes, Turner noticed an empty envelope that the suspect had been carrying in a pocket. Makki told detectives that the envelope had held cash.

The next day, investigators returned to the crime scene with a search warrant. They found Mark Makki's wallet in the same room where he told investigators his mother hid valuables.

He had previously told detectives that he had lost his wallet several days before.

Detectives again interviewed Makki on Sunday. He told them the envelope they had seen when he gave them his clothes came from his mother's hiding place.

"The defendant stated that he took the envelope some time ago and spent the money," Turner wrote.

Turner wrote that detectives showed Makki "photographs of significant items of evidentiary value, which were seized at the crime scene. The defendant acknowledged that the items belonged to him." The document did not describe those items.

Makki also recanted his earlier statements regarding where he had been Thursday, the charging document said.

Makki was being held at a Montgomery jail yesterday and could not be reached for comment. It was unclear whether he had retained an attorney.

The suspect is scheduled to appear before a District Court judge in Rockville for a bond hearing this afternoon.

Attempts to reach the victim's daughter and husband yesterday were unsuccessful.

Seyed-Makki did administrative work at her husband's medical office in Greenbelt. He is an ear, nose and throat surgeon, and the couple were well-known in the Iranian American community. They fled Iran in the 1980s.

Mahin Ghadiri, a close friend of the victim's, said yesterday she was stunned by the news of Mark Makki's arrest.

"It's so shocking, because that boy is so innocent," Ghadiri said.

Staff researcher Bobbye Pratt contributed to this report.

Mark K. Makki is charged with killing Shohreh Seyed-Makki.