The first weeks of school don't only bring the start of classes and keg parties. They also usually bring an increase in crime.

This year was no exception.

Last week alone there were six robberies in Ann Arbor, mostly in student areas - a dramatic increase from the four-week stretch before that, which saw only two robberies. At least one student was taken to the hospital as a result. There has also been an increase in nonviolent theft.

Police said the robberies were isolated and do not represent a crime spree. Police also said they have had a high success rate apprehending suspects, arresting three out of the five so far.

"We've been on a roll. We've caught everybody," Sgt. Brad Hill of the Ann Arbor Police Department said. "Sometimes we don't catch anybody."

Hill said an increase in crime is not unusual in the weeks after students move in. During the same period last year, there was only one fewer robbery and one fewer breaking and entering incident. There were 12 cases of breaking and entering last week.

Last Monday, a man began a series of robberies near the 1500 block of Patricia Avenue at about 11 p.m., when he pounded on a door, claiming he'd been stabbed, they left when the resident told him to go around to the front.

Police suspect he was involved in two more incidents, the first at about 1 a.m. A 21-year-old student living on the 800 block of Arch Street said she heard noises on the floor below around that time. She went to the stairway and saw the man look up and begin to walk toward her, police said.

He pressed a butcher knife to her stomach and demanded money. She gave him her wallet and he left. Police said the suspect entered by cutting through a dining-room screen.

At about 1:20 a.m., a 20-year-old University student was on his front porch on the 1000 block of Packard Street when he was approached by a stranger. The man jabbed the student in the stomach with a butcher knife. The victim tried to run, but stopped, hindered by his flip-flops. He told suspect that his money was inside his home. The robber then followed him past several roommates and into his bedroom, where he handed over the $7 in his wallet. The victim sustained a superficial cut on his stomach.

Police used tracking dogs to find the man, who was hiding under a BMW on the 1000 block of Oakland Street.

Another robbery occurred last Wednesday at about 10:45 p.m. on the well-lit 200 block of North Ingalls Avenue.

A female University student was walking home from a coffee shop listening to her iPod. The 18-year-old was attacked from behind by two men and struck in the head with a foot-long metal pipe.

The men held the victim down and hit her several more times before they stole her wallet and fled, police said. Police officers were flagged down and found assailants below the Broadway Bridge using tracking dogs.

One was a 25-year-old male Ann Arbor resident and the other was a 20-year-old man from Santa Fe, N.M. The victim has been released from the hospital.

Since student move-in, there have also been reports of sexual prowling, several of them at sorority houses. Last Wednesday, at the Alpha Phi sorority on Oxford Street, sorority members spotted a man on their fire escape at about midnight. He ran when they started shouting at him. Members told police the incident was similar to others that had happened at the sorority. On Sept. 8, a man broke in to the Alpha Chi Omega sorority on Hill Street and started to massage a woman's back while she lay sleeping. When she screamed, he ran. On Aug. 27, an intruder was discovered in the Alpha Delta Pi sorority house on South Forest Avenue. AAPD Detective Sgt. Richard Kinsey said the events are probably not connected.

Johanna Soet, director of the Sexual Assault Prevention and Awareness Center, emphasized that "you should follow your internal clock and what you think is safe or not."

Soet said there is usually an increase in sexual assault reports in the first weeks of school. She said an especially significant number of those are reported by freshman girls.

Alcohol is involved in 75 percent of all sexual violence cases at colleges, Soet said.

Charlotte DeMatteo, an AAPD crime statistician, advised that students pay special attention to locking windows - even those with screens - and should always lock, rather than just close them.

Kinsey said students should lock upper-level windows, especially if they're near a fire escape.

"This is a university town and it does attract thieves, prowlers, you name it," he said.