A man walking his dog found the body after residents in the area reported hearing an explosion.
The incident began in the 1000-block of Sherman Avenue around 4 a.m. when several residents reported hearing a very loud explosion. Police searched the scene but found nothing suspicious.
Then, around 5:45 a.m., resident Dale Wyatt made a gruesome discovery while walking his dog in Fitzsimmons Park: the headless body of an adult white male.
Police returned and found what authorities described as a pipe bomb near the body. They started evacuating residents and called officials who canceled classes at Nichols Middle School, 800 Greenleaf Street.
Around 9:30 a.m. the Cook County bomb squad detonated the possible explosive device. Police and the bomb squad spent the rest of the day combing the park, mere yards from the school.
"We take this extremely seriously and at this point our investigation continues and not only involves the Evanston Police Department but the county and the Federal Bureau of Investigation and the A.T.F.," said Commander Tom Guenther, Evanston Police Department.
Police haven't released the name of the dead man, who they say was known to another police agency. On Tuesday, they searched his apartment in the 1000-block of Main Street as well as his computer.
"He seemed like a nice guy," said neighbor Peter Wolf. "He had a girlfriend and once in a while they'd smoke cigarettes in the front door."
Police said they found no suicide note in the man's apartment or near the man.
Evanston police removed boxes of evidence from his apartment on Tuesday. The apartment is about two blocks away from the site of the explosion that apparently decapitated the man.
"It was a humongous bang - it shook my house," said resident Becca McKay. "It was unlike anything we'd ever heard."
Police are classifying the case as a death investigation, despite initial reports describing it as an apparent suicide. Police have not determined whether the explosion was accidental or intentional.
"This is obviously a highly unusual situation and we should be vigilant and pay attention if anyone sees anything unusual. They should make a point of raising that," said 4th Ward Alderman Don Wilson.
"I had no idea I was going to stumble across a dead body. It freaked me out, it did freak me out a little bit. I thought it was a sick practical joke at first. I thought it was a mannequin until the other lady came by and said it looked really real to me too. Then we decided, OK, we're both gonna call the cops," said Wyatt.
The neighborhood is described as quiet, family-friendly, and bustling with children.
"I personally think it's kind of disconcerting, it's alarming," said neighborhood resident Graciela Shelley.
Investigators were on the scene gathering evidence Tuesday afternoon. Nichols Middle School will be closed again on Wednesday.
Officials say they still have a lot of work to do processing the scene of the explosion and having students around seems inappropriate given the circumstances.