In a press conference Tuesday afternoon, the San Francisco Police department released video footage of a group of suspects of three men who beat a homeless man to death last week in the Financial District.

67-year-old Tai Lam was beaten to death as he slept in an alley near Sutter and Montgomery Streets late the night of Sunday, November 23. He was discovered, still in his sleeping bag, at around 7:30 Monday morning.

Lam, who the Ex reports "weighed less than 100 pounds and stood at 5-foot-5," kept to himself and was not troublesome, according to merchants and others who frequented the area.

According to Bay City News (via ABC7), SFPD Sergeant John Cagney "said that business owners who knew Lam said he was very clean and never caused any problems. All who knew him said he was a very respectful gentleman."

Disabled for some time, the crutches he used to get around were found less than five feet from his remains, the Chron reports.

So, who are the men who police say attacked Lam twice, without provocation? Take a look:

The above is surveillance footage of the three suspects as they took a smoke break on the steps to Crocker Galleria near Montgomery and Post Streets, right before they began to beat Lam to death, SFPD Lieutenant Toney Chaplin said Tuesday.

The Chron reports that Chaplin believes the men "attended an event in the neighborhood," then, at around 11 p.m. on Sunday the 23rd, they had a brief chat with a Crocker Galleria security guard, stopped for the smoke you see above, then set upon Lam.

According to Chaplin, there is additional video footage of the men during the attack that has not been released because it was "too violent and graphic."

The men walked away following the initial attack, then returned a second time, kicking and beating Lam again.

"He was unable to defend himself. He died alone after suffering these horrendous attacks," Chaplin said at the press conference.

In a second video, the suspects can be seen kicking Lam. It's a disturbing bit of video, so please consider that before you watch it:

Cagney says that the men in the video did not appear to be homeless themselves. Two of them are believed to be African-American and a third appears to be Caucasian, all in their late teens to early 20s or 30s, wearing hooded sweatshirts and baggy clothing. One of the African-American suspects appears to be more than 6 feet tall, Cagney says.

Police say they suspect that the men took BART or Muni to or from the location of the homicide, and will be canvassing the Montgomery Street BART and Muni Metro station with fliers in an effort to track down the suspects.

“There was no reason for this,” CBS5 quotes Chaplin as saying.

“As far as provocation goes, I don’t know how much provocation you can give someone sleeping in a sleeping bag with your crutches a few feet away from you.”

Police are still seeking additional video surveillance footage or information about the three men. Anyone with information on this case or suspects is urged to contact Cagney, the lead investigator on the case, at 415-734-3181or by email at [email protected]

You can also contact SFPD via their anonymous tip line at 415-575-4444 or send a tip by text message to TIP411 with “SFPD” in the message.