Suspect Has Witness that Doesn't Lie: His Metrocard

In the computer world you are used to perfect security or it's useless. It's not like that in most fields though.

the metrocard itself cannot be used to identify a person's whereabout; however, it can be used to constrain the movement

the key word in that article is "physically" ... the metrocard data is used to determine how physically plausible an action is

for example, one uses metrocard at 9amET in new york, then someone get killed in LA at 10amET, s/he can't be physically possible candidate even if ALL govt witness say so

of course, orthogonal info help too, a phone call at 930amET or even 705amET ATM withdrawal (with pic)

Bus to "Payomatic".

Buddy cashes check, photograph taken, Jones visible in background of photo.

Subway to girlfriend.

So everything fits. The truly scary part of the story:

During the interrogation, he said, it occurred to him that he had used his MetroCard on the bus and the subway, and he asked the police to check it. A detective took the card briefly, and then gave it back to him, and there was no further discussion about the card, he said.

just in case