HOUSTON --Investigators say a man is preying on women on the northwest side of Harris County. The Sheriff's Office Wednesday released a sketch of the suspect who they say raped at least three women in a string of crimes dating back to 2007. The suspect used a box cutter to frighten his victims and he may have stalked them, authorities say. One victim said she had seen him before. "He had contact with her several times so we know he was watching that area. But then again, that's speculation," said Sgt. Michael Weinel of the Harris County Sheriff's Office. The first rape happened on the track at Spring Woods High School off Gessner on a Saturday in August 2007. The victim was running on the track around 1:30am when the man attacked her. "The victim was not a student or an employee of the school. It was a random attack. We haven't had anymore attacks like that since this one," said Officer Mark Brown of the Spring Branch ISD police. The second rape happened more than three years later, in November 2010 at the Harpers Mill apartment complex in the 16000 block of Kieth Harrow near Highway 6. The third attack occurred on December 14 just a few miles away in the 5700 block of Timber Creek Place Drive at the Madison apartments, also near Highway 6. Both of the 2010 rapes happened in the laundry rooms around 10:30pm, and in both cases the victims said that was not their normal routine. Even though the first crime happened three and a half years ago, investigators didn't link them until DNA evidence uploaded into a national database connected them late last month. "The person either joins the military and is gone for a while or he goes to prison and he's gone for a while on a separate unrelated charge, and all of a sudden he's released," said Lt Ruben Diaz of the Harris Co. Sheriff's Office. Now authorities want to catch him before he rapes again. "There is no way to know that he's not still out there doing this. We don't know if there are any other victims who haven't reported it," Lt. Diaz said. The suspect is described as a black male, about 5 foot 4, with a stocky build. Authorities say the suspect appears to target Hispanic women in their early 20s. Two of the victims said he drove a white Ford Expedition with chrome bumpers. He has also used similar methods in each attack. "In all three cases, his weapon of choice has been a box cutter. So if there's any other women out there that have been attacked and they know their attacker used a box cutter, please give us that information because it might be the same guy. He used one typically that folds out and locks in," said Lt. Diaz. If you have any information on this case, you are asked to call Crime Stoppers at 713-222-TIPS. You can remain anonymous and could be eligible for a reward.