Ann Arbor police are now reviewing at least 600 tips related to a string of six attacks on women in the city this summer, Det. Sgt. Brian Jatczak said.

The attacks, including two rapes, were reported between July 15 and July 26.

So far, no arrests have been made and no charges have been filed.

Police released the above wanted poster in connection with the sexual assaults.

Many of those he has received are duplicates of those given to city police, he said Tuesday, but new tips continue to come in.

Authorities have said one or two men are believed to be responsible for the attacks, each of which involved a young woman walking alone late at night or early in the morning. Two of the attacks occurred near the University of Michigan’s central campus.

A multi-jurisdictional work group has formed this summer to investigate. That group includes members of the Ann Arbor Police Department, University of Michigan Department of Public Safety, Washtenaw County Sheriff’s Department, Michigan State Police and the FBI.

Here’s a list of the attacks:

10:10 p.m. July 15 — A 21-year-old University of Michigan student was walking near Thompson and East Liberty streets when a man grabbed her around the neck. She resisted, broke free and was not injured. The attacker was described as white, 29 years of age, 5 feet, 7 inches tall, 165 pounds, with a medium build.

11:11 p.m. July 15 — A man grabbed a 19-year-old Ypsilanti woman in the 400 block of North Division Street near Community High School and attempted to pull her into a secluded area, but she got away. The attacker was described as 20 to 30 years of age, 5 feet, 6 inches to 5 feet, 7 inches tall, 175 to 200 pounds and clean shaven. He had short, straight black hair and olive skin.

2 a.m. July 16 — A man grabbed a 22-year-old Ann Arbor woman from behind in the 900 block of Greenwood Avenue, lifted up her dress and fondled her before she broke free. The man was described as 5 feet, 6 inches tall with an olive complexion. He had no facial hair and was wearing a zipped-up black hooded sweatshirt and khaki cargo pants.

12:40 a.m. July 18 — An 18-year-old Ann Arbor woman was pulled into an alley and raped in the 700 block of South State Street near the University of Michigan. The attacker was described as white, 20 years of age, between 5 feet, 6 inches and 5 feet, 10 inches tall, with brown hair and brown eyes. He was wearing a green T-shirt and khaki cargo pants.

10:30 p.m. to 11 p.m. July 18 — A man followed a 26-year-old Ypsilanti woman into an elevator in the Liberty Square parking structure and raped her. The attacker was described as white, 26 years of age, 5 feet, 6 inches to 5 feet, 7 inches tall, with short, dark and straight hair, police said.

11:30 p.m. July 26—A 21-year-old University of Michigan student retrieved something from her car in a parking lot in the 700 block of South State Street when she was grabbed from behind and fondled by a man, before breaking free, police said.

Crime Stoppers is offering up to a $1,000 reward for information leading to an arrest in any of the attacks. Jatczak encourages anyone with information to call police. People can call the Ann Arbor Police Department's tip line at (734) 794-6939 or Crime Stoppers at 1 (800) SPEAK UP.

Heidi Fenton covers police and courts for AnnArbor.com. Reach her at heidifenton@annarbor.com or 734-623-4673. You also can follow her on Twitter or subscribe to AnnArbor.com's e-mail newsletters.