It becomes clear early on in the series that the mutagen which transformed the Turtles and Splinter into their new forms was dumped into the sewers by Shredder in an effort to murder Yoshi, as he had mistakenly believed it to be a deadly poison rather than a transformative agent. After several years of training under Splinter, the Turtles set out to find whoever is responsible for their transformation, and upon learning that Shredder was behind it, they vow to put an end to his ongoing criminal career and restore Splinter back to his human form. Along the way, they rescue and befriend Channel 6 news reporter April O'Neil, who becomes one of their strongest allies. The Turtles, who had rarely left the sewers prior to meeting April, also began to take on the role of semi-vigilante crime fighters. Despite this, they frequently have to deal with citizens misunderstanding them, largely due to the efforts of Channel 6 newsmen Burne Thompson and Vernon Fenwick, who both distrust the Turtles and frequently and wrongfully blame them for the trouble that Shredder and Krang cause. As a result, they mainly have to rely on April (either via Turtle-com, or Channel 6 news reports) to inform them of crimes in the city, and to counteract Burne and Vernon's smear and bad-tempered campaigns against them with her own news coverage of the Turtles, portraying them as a force for good. Reluctant to expose themselves to the outside world, the Turtles initially wear disguises whenever they leave the sewers, although this is slowly relaxed as the series progresses and they gain the trust of the broader populace, whom they have saved from Shredder and other villains on many occasions.