An NYPD investigator with direct knowledge tells The Daily Beast that whoever built the pipe bombs sent to prominent Trump critics sought to make the devices more deadly by mixing bits of metal and glass in with the black powder.

The absence of any obvious triggering device makes some experts who have only seen the X-rays of the devices wonder if they were meant to detonate. But the NYPD investigator notes that any one of the devices could have been detonated had somebody jostled it or fiddled with it in an unfortunate way.

After seeing a news photo of one of the packages, a private security executive realized that he had chanced to playfully toss an identical package in the air without realizing what it was. He immediately notified New York police, who determined that it was indeed one of the bombs.

Nobody can rightly doubt that the bomb maker intended to spread fear if not actual physical injury.

And with the device sent to Robert De Niro on Tuesday, it became clear that the targets were not just those who have been vilified by the far right.

De Niro is not a political figure in the way of the other targets. But he has been one of the more vocal—and profane—critics of Trump. An explosive device sent to the actor was almost certainly the result of an impulse either to defend Trump or to frighten those who oppose Trump or both.

In the meantime, experts questioned whether the timers included in at least two of the devices were actually triggering mechanisms, particularly given the unpredictability of when the package would actually reach its destination.

Experts were also struck by the use of just a single penlight battery, hardly a reliable way to ensure the bomb would detonate when it finally got to where it was intended.

Otherwise, the devices were constructed in keeping with pipe-bomb tradition.

“It is put together in the proper way,” the NYPD investigator said.