All the synaptic gospels (Matthew, Mark, Luke and John) were probably not written by the Apostles directly. Mark was probably written 40 years after Jesus's death and resurrection (and he and Luke were not apostles). John was the latest and written probably 100 years after Jesus's death. The only original Apostle to actually write anything down was probably Peter and he only wrote down 2 Peter (1 Peter was probably done by a scribe).
Mark for example recounts Jesus death in the first person. So, it's written as if he witnessed it himself.