Michael Boone attends a fundraiser for him at Trusty's, a bar on Capitol Hill where Michael works as a bartender. He was stabbed April 30 while trying to intervene in the robbery of a bar patron as he walked her home, and has been out of work since. (Astrid Riecken/FOR THE WASHINGTON POST)

Michael Anderson heard the bloodcurdling scream as he sat in his office at the Patton Boggs law firm in Georgetown. He looked outside his window and saw a man on M Street NW dragging a woman by her hair.

Anderson bolted down five flights of stairs, dashed into an underground parking garage and confronted the assailant, who had released the woman and was reaching for something in his backpack. Anderson grabbed the man’s head and, with the help of four other good Samaritans who had come running, subdued him until police arrived.

Anderson and the others were recently awarded Citizen of the Year medals by D.C. Police Chief Cathy L. Lanier for their “fearless display of bravery and concern.”

Their actions stand in stark contrast to those of the employees at the Apple store in Bethesda, who heard screams coming from the Lululemon Athletica store next door in March 2011 and did not respond or call police. Jayna Murray was murdered inside the store in a brutal attack by a co-worker, Brittany Norwood.

But encouraging people to help stop crimes in progress is a tricky business fraught with potential danger, criminologists say. Trayvon Martin’s death in February at the hands of a neighborhood watch volunteer in Florida, George Zimmerman, who claimed that he shot the unarmed teenager in self-defense after a scuffle, is an example of all that can go wrong if people take the law into their hands.

Closer to home, people who intervened to stop two recent purse snatchings met with very different outcomes. One was awarded a Chief of Police Special Award by Lanier for risking his life “to apprehend a dangerous individual.” The other awoke in intensive care with eight stab wounds, a collapsed lung and slashes on his face and hands, lucky to be alive.

Lanier said last week in an interview that she values community involvement and hopes the District never has a case like that of Kitty Genovese, who was killed outside her apartment building in Queens in 1964, a case that has come to symbolize public apathy. Numerous people in the neighborhood heard her struggle, but no one helped her.

But heroism, Lanier said, is scribbling down a license plate number in a carjacking or following a street robber from a safe distance after calling police. In extreme circumstances, she said, people have to act to save neighbors or strangers from physical harm. “That’s what our community should do for each other,” Lanier said.

What people shouldn’t do, she said, is put themselves in harm’s way to protect personal property or money. “It’s not worth getting stabbed or shot,” she said.

James Alan Fox, a criminologist at Northeastern University in Boston, said police want to encourage people to provide information and call 911, Fox said, “yet there is a danger for them overdoing it.”

“Innocent people can get hurt,” he said. “The police are trained to know what to do and when to do it. The public is not.”

For Anderson, the Patton Boggs lawyer, doing nothing was never an option.

“Anybody who heard that scream would have done something,” he said.

After bounding down the stairs, he and the others who heard the screams chased the attacker into the parking garage, where he let the woman go. They pursued him and found him hiding beneath a car. Robert Petris had heard the woman’s screams as he walked his Labrador retrievers. He, too, responded. So did Suthima Malayaman, who, like Anderson, rushed down to the street from her Patton Boggs office.

Anderson remembered wondering to himself: “The man was capable of attacking a woman in broad daylight. What might he do next?”

Moments later, the attacker crawled out from under the car. When he reached for his backpack, Anderson grabbed the man’s head and swung his knee into him. “I think he sort of knew the game was over,” Anderson said.

Several people had called D.C. police. Petris and Malayaman waited with the victim until police arrived and arrested Juan Carlos Lopez-Jimenez, 20. He pleaded guilty and was sentenced to 20 months in prison for attempted kidnapping and 150 days for assault, according to court documents.

For their actions, Lanier conferred Citizen of the Year awards in March on Anderson, Petris, Malayaman, Glen Hackbarth and Ann Donohue.

Timothy Gleason also heard a woman screaming, “They stole my purse! They stole my purse!” He was walking his dog one night in February in an alley off the 1700 block of New Jersey Avenue NW when he saw young men followed by a woman, blood pouring from a split lip, in hot pursuit. One of the men clutched the woman’s purse.

Gleason joined the chase, trapped the man with the purse, tackled him into a fence and put him in a headlock. Another neighbor helped secure him, and other neighbors came outside and called police, who arrived within minutes and put him in handcuffs.

The man he subdued, Raymond King, 22, was convicted in the robbery on April 19 and is scheduled for sentencing in June, according to court records.

“Everyone in the neighborhood came together,” said Gleason, a bartender at Union Jack’s in Bethesda. “I just happened to be the closest. It’s something that’s in all of us, I think. You see someone in trouble, you just want to go help them.”

Contrast Gleason’s experience with that of Michael Boone, a bartender at Trusty’s tavern on Pennsylvania Avenue near Capitol Hill. He was walking a woman home from the bar on the night of April 30 when a man leapt from the bushes and snatched the woman’s purse. Boone snatched it back. The man responded furiously, and they wrestled on the sidewalk.

The fight lasted only about a minute before the man disappeared. Boone gathered himself and rose to his feet. The woman screamed.

Boone hadn’t seen the attacker’s knife, nor did he realize that his body was covered in blood.

“I told her immediately, ‘There’s a lot of blood. We need to call 911,’ ” said Boone, 38. “I eventually collapsed. That’s the last thing I remember until the next morning.”

He’d been stabbed eight times. His hands and face were slashed; one thrust collapsed a lung. Authorities told him he was airlifted to a hospital by helicopter, rescuers uncertain he would survive.

Doctors stopped Boone’s internal bleeding, and he began to recover.

“I’m really lucky to be alive,” he said.

Police arrested James Moyler, 43, and authorities charged him with assault with intent to kill and robbery.

After his release from the hospital, Boone held forth from a bar stool at Trusty’s. He has no health insurance and isn’t sure when he’ll be able to go back to work.

“I have no regrets,” he said, recalling the attack.

“You’re a [expletive] hero,” one man exclaimed.

Adam Maradian, Trusty’s manager, agreed, remarking that Boone had risked his life for a purse that contained just a few dollars.

“It’s stupid, to be honest,” Maradian said. “But he would do it again, I’m sure.”