Answer:
Maritime marauders
My second is performed by my first, and it is thought a thief by the marks of my whole might be caught.
In spring I look gay, Covered in a green array, The warmer it gets the more clothing I wear, As the cold grows, I throw away my clothes.
In a year, there are 12 months. Seven months have 31 days. How many months have 28 days?
I start in little but I end in full, you'll find me in half and complete.
I am a rock group with four members. All dead one was assassinated.