PITTSBURGH (KDKA) — Shakespeare said it well: “April is the cruelest month.”

April 15 – an unforgettable tragedy Monday in Boston.

READ MORE: Mt. Oliver Police Department Cracks Down On Drug Crimes After Months-Long Investigation

April19, 1995 – Timothy McVeigh sets off a truck bomb in Oklahoma City.

April 19, 1993 – 76 people die, 20 of them children in a siege at the Branch Davidian complex in Waco, Texas.

Monday was “Patriots Day” in Boston. Did the bomber know?

“Again, it helps send their message. It’s all about propaganda,” said Larry Likar, a former FBI profiler.

Likar is now a professor at La Roche College.

Understanding the language of terrorism is only one consideration as investigators attempt literally to pick up the pieces.

“They’re almost like huge vacuum cleaners when they go on a bombing crime scene; everything comes up,” said Likar.

In the Unabomber case, agents detected a signature in Ted Kaczynski’s mail bombs.

“If it’s unique, similar material that’s used in different types of bombs, that’s when they’re referring to signatures,” Likar says.

READ MORE: Parents Of Woodland Hills High School Students Concerned About School Safety Following Another Threat

The bombs used at the marathon finish line are said to be shrapnel like – nails, BBs and ball bearings – packed in a pressure cooker with possibly an electronic timer.

“That’s basically a version of a pipe bomb,” Likar adds.

But Likar says that doesn’t mean the bomber lacked sophistication.

“What’s sophisticated so far is what looks like very good operational security. If there are no leaks, if we don’t hear of anybody rounded up in the next couple of days – that’s sophistication,” says Likar.

In Boston, they will be tracing everyone who recently bought a pressure-cooker, and hoping for any break.

Timothy McVeigh was arrested during a traffic stop after the federal building bombing.

Patience is critical.

“The Unabomber took years,” Likar adds.

Unless there is some luck involved, it will be a long time before the investigation in Boston is over.

Runners Still In Shock After Boston Marathon Bombings (4/16/13)
More Reports on the Boston Marathon Bombing

MORE NEWS: Remember, Reflect At Tree Of Life: Commemorating The 11 Lives Lost 3 Years Ago In Synagogue Shooting

Join The Conversation On The KDKA Facebook Page
Stay Up To Date, Follow KDKA On Twitter