Police described victim Tai Lam, 67, as a ‘defenseless senior citizen’ with disabilities, who weighed less than 100 pounds and stood about 5 feet 5 inches tall

Police have released surveillance footage showing a group of men who they suspect of savagely beating a homeless man to death as he slept in an alley in downtown San Francisco.

Tai Lam, 67, was found dead last Monday in an alley behind buildings near the corner of Montgomery and Sutter streets. He was still inside his sleeping bag.

Police described Lam as a ‘defenseless senior citizen’ with disabilities, who weighed less than 100 pounds and stood about 5 feet 5 inches tall. He was not robbed, and there was no clear motive in the attack.

Police spokesman Albie Esparza has described the incident as 'a vicious, unprovoked attack by these coward suspects.'

Video surveillance shows a man kicking Lam’s sleeping bag. Police said the man and two others returned a short time later to beat him again.

‘There was no reason for this,’ said San Francisco Police Lt. Toney Chaplin. ‘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.’

The attacks happened between 11pm and midnight on Nov. 23, but Lam's body wasn't discovered until about 7am the next morning.

‘He was unable to defend himself. He died alone after suffering these horrendous attacks,” Chaplin said.

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Police have released surveillance footage showing a group of men who they suspect of savagely beating a homeless man to death as he slept in an alley in downtown San Francisco

The newly released video shows the three persons of interest while they smoked a cigarette on the steps to Crocker Galleria near Montgomery and Post streets, shortly before the assaults.

The three young men are wearing hooded sweatshirts and baggy clothing and did not appear to be homeless themselves. They were described as possibly in their late teens to early 20s or 30s.

Two of the suspects are believed to be African-American while the third is believed to be Caucasian. One of the African-American males appeared to stand more than 6 feet tall.

Police are asking anyone with video surveillance of the area or anyone who may have additional information about the three suspects to contact San Francisco police investigators.