PALO ALTO -- Authorities believe a graduate student who was robbed at gunpoint Monday night was at least the fourth victim in a string of robberies reported in the Palo Alto and Stanford area.

The incident occurred around 11:30 p.m. Monday on the Stanford University campus near the intersection of Escondido Road and Campus Drive, according to Sergeant Hilary Karp of the Stanford Department of Public Safety.

A male graduate student was walking to his on-campus housing when three men, one armed with a handgun, approached him and demanded money. The men took cash and a cell phone and left in a newer-model red sedan, Karp said.

The victim, who was not injured in the robbery, described all three as black, clean-shaven men in their middle 20s. The suspect holding the gun was between 5 feet 5 inches and 5 feet 7 inches tall and between 240 and 250 pounds. He was wearing a hat, jean shorts or pants and a white T-shirt with a logo on the front.

A second suspect was also wearing a hat as well as a dark flannel shirt and long, dark baggy pants. The second man is taller than the first with a skinny build. A third man was only described as 5 feet 5 inches tall to 5 feet 7 inches tall with a medium build.

Karp said there was "a lot of consistency" between this robbery and other incidents in the area except that there was one more suspect involved in this latest incident.

In the first Stanford robbery, two men approached a 21-year-old undergraduate student as she was walking to her car in the campus parking lot outside Toyon Hall around 10 p.m. Wednesday. The men chatted with her briefly before one pointed a handgun at her and took her money without injuring her.

Another similar robbery occurred just 40 minutes later in Palo Alto.

The victims were in their parked vehicle in the 400 block of Hawthorne Avenue when two men, each armed with black handguns, approached them and demanded money.

One of the victims was struck on the side of the head by one of the robbers, but was not significantly injured. The assailants got away with a wallet belonging to one of the victims, according to police.

Karp said people out after dark should be especially careful to travel in pairs or groups and be aware of the surrounding area.