Did the disciples lie?
You can say the disciples hallucinated or were somehow deceived themselves, but it's very difficult to call them liars. As we saw in the section on voluntary sufferings, the disciples so sincerely believed that Jesus rose from the dead that they changed their whole way of life. They labored, they suffered, and in many cases, they died quite willingly for what they believed.
James and Paul, yet again
James and Paul came to believe not based on what they heard, but what they believed they were eyewitnesses to. So a possible conspiracy of the disciples doesn't account for their conversion.
Liars make poor martyrs
You might say that being willing to die for one's beliefs doesn't verify those beliefs are true. And you'd be right. Atheists have died for communism. Jihadists have died in the name of their religion. But the claim here is different. Willingness to suffer and die for your beliefs means you strongly believe them, but in the case of the disciples their beliefs were formed not by what someone else told them, but what they were eyewitnesses to.
From a man who knows something about conspiracies
“I know the resurrection is a fact, and Watergate proved it to me. How? Because 12 men testified they had seen Jesus raised from the dead, then they proclaimed that truth for 40 years, never once denying it. Everyone was beaten, tortured, stoned and put in prison. They would not have endured that if it weren't true. Watergate embroiled 12 of the most powerful men in the world and they couldn't keep a lie for three weeks. You're telling me 12 apostles could keep a lie for 40 years? Absolutely impossible.”
- Chuck Colson. Served as Special Counsel to President Richard Nixon from 1969 to 1973. An evangelical leader who founded Prison Fellowship.