Details from http://aceattorney.wikia.com/wiki/Ema_Skye
Ema Skye is a forensics-obsessed detective in the Los Angeles Criminal Affairs Department. She happens to have been in charge of the same cases that defense attorney Apollo Justice handled. She was also Phoenix Wright's investigative partner and co-council in the murder of Bruce Goodman, nine years before she became a detective.
Ema Skye is responsible for introducing forensic investigation techniques to Wright and Justice.