PHILADELPHIA -- NBC 10 News has learned that two people have been arrested and charged in the murder of a parking lot attendant.

William Palmer (pictured), 18, was shot and killed during a robbery attempt Tuesday at Hahnemann University Hospital.

On Friday, police arrested Len Ellis, 23, and Zairer Thompson, 19. Both men have been charged with murder, robbery, conspiracy and related offenses.

Police said they also believe one of the two people they are questioning could have connections to a series of parking lot robberies throughout May.

"His mother was police officer. His father was a police officer. His stepfather was a police officer. It just shows that we're just as susceptible to violence as anyone else," said Philadelphia Police Commissioner Sylvester Johnson.

Without citing specifics, investigators admitted that they are checking another robbery that occurred at Hahnemann Hospital.

"Certain names have surfaced within received tips with the same type of information that basically led us to focus our efforts on these people. We looked at a previous robbery and were able to identify these people from a previous robbery and that's what focused us on them," a police officer said Friday.

Palmer's funeral is scheduled for late next week.