Please help me understand this (English is not my 1st language)?

In the novel Without Remorse by Tom Clancy there's this part where John Kelly's (protagonist) wife and her unborn baby die in a car crash. John Kelly goes to the hospital with no luck only to find out that both his beloved wife and the baby are now dead. But I'm having a hard time trying to understand... show more In the novel Without Remorse by Tom Clancy there's this part where John Kelly's (protagonist) wife and her unborn baby die in a car crash. John Kelly goes to the hospital with no luck only to find out that both his beloved wife and the baby are now dead. But I'm having a hard time trying to understand the following passage, so please help me understand it?

Here is the original context:

"He walked out of the emergency room, people's eyes on him, doctors and nurses. A priest had been called to perform his last duty, and had said a few things that he knew were unheard. A police officer explained that it hadn't been the driver's fault, the breaks had failed, mechanical defect, nobody's fault, really. Just one of those things. All the things he'd said before, on other such occasions, trying to explain to some innocent person why the main part of his world had just ended, as though it mattered. This Mr. Kelly was a tough one, the officer saw, and all the more vulnerable because of it."

What does this last sentence mean? "This Mr. Kelly was a tough one, the officer saw, and all the more vulnerable because of it."
What does it mean?
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