Subscribe for 99¢

UPDATED at 9:30 a.m. Monday with details from St. Louis police

Police on the campus of Washington University have issued a crime alert after a series of armed robberies, including two in which armed gunmen punched students.

Police are warning students to be alert and carry a whistle to summon help, among other precautions.

Campus police said there were four robberies since Friday. The latest three were within minutes of each other on Saturday night, in the Skinker-DeBaliviere neighborhood.

Washington University issued the crime alert Sunday because the crimes happened on or near campus. "The criminal activity is believed to present a serious or continuing threat to students and employees," the alert said.

Washington University's police department increased patrols with more officers in the neighborhood. Security would help escorts students walking to their apartments after parking, the university said. Meanwhile, the campus police issued a list of precautions. They include: Do not sit in a car to text or use electronic devices, and run in a different direction if being followed.

St. Louis police on Monday said they have made no arrests but released detailed descriptions of the robbers and say officers have found some of the victims' belongings.

The three Saturday holdups happened between about 11:30 and 11:45 p.m. In one case, two Washington University students were walking near Westminster Place and Laurel Street when two men armed with a handgun took the students' property. The victims were 22-year-old women.

A second robbery Saturday was in the 5800 block of Pershing, campus police say. This victim, a 21-year-old man, was not affiliated with the university.

A third robbery Saturday, in the 6000 block of Pershing, involved a 27-year-old man who is a Washington University graduate student. He was sitting in his car with the window open. According to campus police, one of the robbers punched the student through the window, opened the car door and took the student's belongings. The robbers went to a parked car nearby and drove off.

One robber is a black man, 20 to 25 years old, 5-foot-10 to 5-foot 11 and weighing 130 to 150 pounds. He had a dark complexion, short hair and a mustache. He wore dark clothing. The second robber was also black and also 20 to 25 years old. He was 5-foot-10 to 6-feet tall and 130 to 150 pounds. He also had a dark complexion, short hair and a mustache and wore a dark shirt, red athletic shorts and dark shoes. The robbers took cell phones, bag or purse and credit cards at gunpoint.

The robberies were similar to the one in which the male student was punched and robbed at gunpoint at about 2 a.m. Friday, authorities say. That crime was in the 6000 block of Westminster Place. The victim, 21, had just parked and got out of his vehicle. He was approached by two men. One of the men pointed a gun at the victim, while his accomplice removed the victim's backpack and emptied the victim's pockets, St. Louis police say.

The suspects "punched the victim several times" and drove off in a dark sedan, St. Louis police say. The victim was hurt but declined medical treatment, police say.

The victim from Friday described his attackers this way: the one with the gun was a black man, about 26 years old, 5-foot-10 with short hair and wearing a black sweatshirt. The accomplice was a black man in dark clothing, but police had nothing more specific.

St. Louis police say that a cell phone belonging to one victim was found in the 6000 block of Pershing, a stolen bag was found in the area of Rosedale and McPherson avenues and another victim's purse was found near Shenandoah and Klemm avenues.