Prosecution investigators have seized evidence on an alleged secret stock sales contract between SK Group and JP Morgan. Prosecution officials said they had come upon the evidence on Monday after searching through company offices of SK Group. They said they are considering summoning top-level executives including SK Corporation Chairman Chey Tae-won and SK Group Chairman Son Kil-seung after questioning working-level officials. The prosecution has also banned Chey and other sixteen executives from leaving the country as tensions intensified surrounding the probe on the alleged illegal stock transactions. Early in January, civic groups sued SK