Kostrzewski met KAT at the first edition of Silesian Rock Festival in Bytom.

In 1985 KAT released their debut album 666 and its English version Metal and Hell.

Kostrzewski afterwards participated in many musical projects with other Silesian rock musicians.

After several changes in KAT (Jacek Regulski and Krzysztof Oset left), Kostrzewski and the band went on to record the album Bastard, which contains the hit song Łza dla cieniów minionych.

The first day after release was an immense success where they played at Jarocin festival (the band sold over 4000 copies).