TCGA files name

[papori]

Hi all,
What is the difference between files that has:
_1
_2
_3
_4
to regular files (.bam) in the TCGA data?

for example:
TCGA-A2-A04T-01A-21D-A128-09_IlluminaGA-DNASeq_whole.bam
TCGA-A7-A0CE-01A-11D-A12L-09_IlluminaGA-DNASeq_whole_1.bam
TCGA-A2-A0D3-01A-11D-A10Y-09_IlluminaGA-DNASeq_exome_2.bam
TCGA-A2-A04N-01A-11D-A10Y-09_IlluminaGA-DNASeq_exome_4.bam

At the begining i thoght that it is single end, but what is _4??
Thanks,
Pap