Dwayne Whitaker, 51, of San Francisco, was sentenced to 439 years to life by San Francisco Superior Court Judge Gail Dekreon for the robberies of four victims in July and August 2008.
Three of the victims were older than 65 and one was 55 years old. In each case, the victim was trailed while walking home -- often with groceries -- and then brutally attacked in an apartment lobby by Whitaker, according to the district attorney's office.
Initially after his arrest in August 2008, police said Whitaker had robbed eight victims between the ages of 68 and 86, including one woman, since earlier that summer.
In the series of attacks, Whitaker allegedly stabbed one victim, struck another with a metal pipe and sent most of them to the hospital. None of the injuries were life-threatening, according to police.
The last man he attacked, a 55-year-old in an apartment building lobby in the 1000 block of Jones Street, was able to call for help and his partner and neighbors responded and restrained Whitaker until police arrived.
Whitaker was arrested after that attempted robbery.
Following his arrest, Whitaker pleaded not guilty and was deemed incompetent to stand trial because of mental health issues.
He was restored to competency nearly five years later in April 2013 and the case went to trial, prosecutors said.
Following the trial, Whitaker was found guilty of burglary, robbery, attempted robbery, assault, elder abuse and receiving stolen property, according to the district attorney's office.
He attempted to plead not guilty by way of insanity, which led to a second stage of his trial, but a judge dismissed his plea, citing lack of evidence, prosecutors said.