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Ars Technica brings us an update to an earlier story in which a court case was thrown out when a police officer's body cam showed him planting drugs before 'finding' them immediately after. Now prosecutors in Maryland are reviewing other body-cam footage and have already thrown out 34 criminal cases with many more under review:
The Baltimore Police Department's body cams, like many across the nation, capture footage 30 seconds before an officer presses the record button. The footage was turned over to defense attorneys as part of a drug prosecution - and that's when the misdeed was uncovered.
[...] "We are dismissing those cases which relied exclusively on the credibility of these officers," Mosby told a news conference Friday. She said the dismissed cases, some of which have already been prosecuted, involved weapons and drugs.
Lesson learned cops - plant drugs, wait 30 seconds, then turn on the camera!
(Score: 0) by Anonymous Coward on Tuesday August 01 2017, @08:39AM (1 child)
How does the device know the button is about to be pressed?
(Score: 2, Informative) by anubi on Tuesday August 01 2017, @09:48AM
It doesn't.
The video part of the camera is always on, endlessly streaming video to a circular RAM buffer ( say, five minute's worth of video ).
Here's the reason... RAM is fast, low power, and can be overwritten over and over without wearing out, but it is volatile. One powerdown and everything's gone. Flash is slower, has to be blocked for writing, and has limited write endurance. But its massive storage capability, and non-volatile. Once written, it stays until deliberately erased and overwritten.
So, upon pressing of the button, there are five minutes worth of video in the RAM buffer previous to the button being pressed. Format that into the blocks required by the Flash ( EEPROM ) memory then continue with the live video stream going into the head of the RAM buffer as the EEPROM is loaded from the tail of the buffer. There has to be RAM available, as the RAM can load a byte at a time from the serial video stream, but EEPROM wants to see the data coming in as chunks.
When played back, the five minutes before the button was pressed will be at the beginning of the video stored in the EEPROM.
Its the same thing that lets you see traces on a digital oscilloscope that happened before the trigger.
So, the magic trick is revealed. No time travel necessary.
"Prove all things; hold fast that which is good." [KJV: I Thessalonians 5:21]