2 more arrested in case of homeless man found beaten and drowned in San Francisco lake

San Francisco police have arrested two more people on in connection with the killing of a homeless man who was found brutally beaten and drowned in a lake.

Michael Grasso, 26, was arrested in San Francisco on Tuesday and jailed on suspicion of homicide and death of an elder adult. Sahmanntha Rundstrom, 19, was taken into custody in Flagstaff, Ariz., on the same day and faces extradition to San Francisco. They join two others who have been arrested in connection with the killing, police said.

About 7 a.m. on May 24, a gardener at Golden Gate Park discovered a body lying face down in Alvord Lake. Detectives determined that the victim was 66-year-old Stephen Williams and that he had been assaulted repeatedly over the course of three days until he was knocked unconscious and dumped in the water.

Soon after the body was found, police identified two transient men believed to be involved in the killing. Niki Williams, 36, who goes by the nickname “Evil,” was arrested that day, and Stephen Billingsley, 19, who goes by the nickname “Pizza Steve,” was jailed the following day.

According to court documents, on May 22, Niki Williams and others allegedly forced the victim into the lake, repeatedly struck him and held his head underwater. The next day, Billingsley and others beat the victim near Haight and Clayton streets, authorities said. The day after that, multiple suspects attacked the victim again, knocking him unconscious and leaving him in Alvord lake, officials said.

A cellphone video obtained by NBC Bay Area News shows multiple men harassing Stephen Williams.

“This is what happens bro,” a voice is heard saying. “That lake, just put him in there.”

Next, the video shows one man pulling Williams by the arm into a lake and dunking him underwater. Their taunts suggest that the group had branded Williams as a sex offender and was punishing him for exposing himself in public.

“How does it feel to … in front of kids?” a voice is heard saying. “That’s why they beat you up, you know that right?”

The medical examiner said that Williams died from multiple traumatic injuries.

Billingsley was charged with murder, torture, conspiracy, elder abuse and assault. Nikki Williams was charged with conspiracy, assault, elder abuse and false imprisonment. They both pleaded not guilty with bail set at $1 million each.

“Although multiple arrests have been made, the investigation continues,” the San Francisco Police Department said in a press release.

The Associated Press contributed to this report.