The suspect in Monday's July 4th parade mass shooting in Highland Park, Illinois, entered a synagogue during Passover in April just a few blocks away from where the massacre would eventually take place, but left shortly after being noticed by security guards and congregants. 

"He entered wearing a yarmulke yet seemed out of place. Upon arriving, he was greeted by our security team, which includes off-duty police officers, and licensed and trained congregants, who observed him throughout," Rabbi Yosef Schanowitz of the North Suburban Lubavitch Chabad wrote on the synagogue's website Tuesday. "A short while later he departed without incident."

Crimo arrest and portrait

Robert Crimo III, 21, was taken into police custody Monday evening. (Katherine Rappel/Inset: Highland Park Police)

The Rabbi told Fox News Digital on Tuesday that authorities have asked him not to discuss the incident. 

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The Central Avenue Synagogue, which is located just a few blocks away from the site of the shooting, had planned to take part in the July 4th parade with a giant menorah on a Chabad float. 

"To the shock and horror of the entire country evil was unleashed on our beloved community, and the celebration of America’s freedom quickly turned into tragedy," Rabbi Schanowitz wrote Tuesday. 

Central Avenue Synagogue

Robert Crimo III allegedly entered the Central Avenue Synagogue in April, but left after congregants and security guards thought he ‘seemed out of place.’ (Google Maps)

The gunman opened fire from a roof around 10:14 a.m., just minutes into the parade, leaving seven people dead and more than two dozen others wounded. 

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A legally purchased "high-powered rifle" was recovered from the scene. Crimo allegedly fled in women's clothes to conceal his facial tattoos and identity, Lake County Major Crime Task Force spokesman Christopher Covelli said. 

He was arrested about eight hours later after a police officer spotted the vehicle he was driving. 

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Crimo, who goes by "Awake the Rapper," allegedly planned the attack for several weeks and left a disturbing social media footprint that includes depictions of a mass shooting in a music video. 

Authorities have not released a motive for the shooting. 

Fox News's Ashley Papa contributed to this report.