SAN DIEGO (CBS 8) - San Diego police are investigating a string of robberies targeting people selling items on Craigslist. Authorities say a black male and a white woman in their 30s are suspected in three robberies that happened Monday night.

San Diego police are investigating a series of robberies within an hour and a half Monday night where several people were robbed of either cash or electronics.

"We've had victims that were buyers and victims that were sellers, so I think that anyone that's using this to make a transaction definitely needs to be aware," SDPD Lt. Andra Brown said.

The first holdup happened after 8:30 p.m. Monday when a woman went to the 200 block of Pardee Street near L Street in Mount Hope to sell an iPad to a man with whom she had been texting to arrange the deal. The suspect pulled out a semi-automatic handgun, took the device and left in an older, small car.

"A black male in his 30s anywhere from 5'8" to 6'1", in all cases though he's described as having some sort of facial hair like a beard or goatee, a black baseball cap, a black shirt or a black jacket and dark pants," Brown said.

At 9:52 p.m. in the 4500 block of 56th Street, $200 was taken from a man in his 20s who had answered a Craigslist room for rent ad. A woman grabbed the cash and jumped into a dark-colored Jeep. The victim suffered road rash while trying to hold onto the vehicle. Paramedics took him to the hospital for treatment of minor injuries.

"He's not Fred Flintstone where he going to be able to stop it with his feet. That was incredibly dangerous. Another option would have been for him to take a step back and get a really good description of the vehicle, including a license plate," Brown said.

Finally, at 10 p.m., police went to the 4100 block of 37th Street near Polk Avenue in City Heights. A man had an iPad stolen from him by a black man matching the earlier suspect description. The robber drove off in a white two-door car with a white woman behind the wheel.

"Blonde hair and I think in some cases he was wearing a dark or a black hoodie sweatshirt. She's described as being 20 to 25 and thin," Brown said.

You may recall on May 11, Mission Beach resident Garrett Berki was killed after meeting three teenagers in Paradise Hills. He was expecting to buy a computer. After being robbed, he was shot as he drove after the trio.