Hulu doc probes whether police could've prevented 2013 Marathon bombing

A new three-part documentary streaming now on Hulu asks a startling question: Could law enforcement have prevented the 2013 Boston Marathon bombing if they'd fully investigated Tamerlan Tsarnaev's role in a triple homicide in Waltham two years earlier?

Zoom in: Local investigative journalist Susan Zalkind was friends with one of the three young men whose throats were slashed and bodies covered in marijuana on the night of Sept. 11, 2011.

• Tsarnaev was named as a suspect in the deaths only after he was killed during the manhunt following the bombing.
• Zalkind investigates what police knew about Tsarnaev in 2011 and the possible misconduct that let him slip away.

What's happening: The series, "The Murders Before the Marathon," bills itself as the first documentary to link the Waltham murders to the marathon bombing.

• "Through [Zalkind's] on the ground reporting, a story emerges of law enforcement failures at every level," according to a press release for the show.

Details: The documentary starts by looking at the Waltham murders, Zalkind's personal connection to one of the victims and the bombing 19 months later that shook the city.

• As the show develops, it explores Tsarnaev's radicalization and the mystery of why his possible accomplice in the murders was shot dead by FBI agents during the bombing investigation.

Deehan's thought bubble: The show is pretty riveting and a perfect way to get through a rainy week.