Georgia State University police are investigating two weekend robberies on or near the downtown campus.

The first incident occurred just before midnight Saturday night, according to a campus crime alert posted on the school's website.

A GSU student and another person, who was not a GSU student, were walking down Edgewood Avenue near Peachtree Center Avenue when they were approached from behind by a man who told them he was armed and demanded money.

The victims gave the thief an expired credit card. They were not injured.

The suspect was described as a white male, about 5 feet, 8 inches tall, wearing a black baseball cap, a black jacket and dark pants.

The second incident, which police described as a "robbery by strong arm," happened about 8:40 p.m.  Sunday at the school's Aderhold Learning Center on Fairlie Street.

"A GSU student reported after leaving the School of Music, he was approached from behind by three unknown suspects right out front of Aderhold Learning Center," police said in a crime alert. The suspects forced the victim to the ground and took his cell phone.

The victim was not injured, police said.

On March 7, a GSU student was robbed of his cell phone and wallet by a man armed with a handgun, according to police.

The suspect in that robbery, which happened just after 5 p.m. on Monday near the intersection of Coca Cola Place and Pratt Street, is described as a black male, 6 feet tall, wearing a dark jacket, baggy blue jeans and having "gold teeth in his mouth and rhinestones," according to the campus crime alert.

A man arrested Tuesday on charges of robbing a passenger leaving the King Memorial MARTA station may also be responsible for the March 7 robbery, which was the latest in a string of incidents in which GSU students were robbed of smartphones.

In an earlier incident, a suspect was arrested on Feb. 15 after a police officer saw him shove a 21-year-old GSU student on Broad Street. According to the police report, student Travis Baker told police Marquavaeous Levon Gray demanded his iPhone and told him he had a gun in his pocket.

Staff writer Rhonda Cook contributed to this article.