Washington ? The former chief of embattled ImClone Systems refused to testify before Congress on Thursday about an experimental drug once touted as miraculous that cost investors millions, raised charges of insider trading and left cancer victims in limbo. But his brother said, “We let patients down.”

Lawmakers called on current ImClone CEO Harlan Waksal and his brother Samuel out on bail from his Wednesday arrest on securities fraud charges to explain how ImClone imploded over its colorectal cancer drug Erbitux.

Samuel Waksal invoked his Fifth Amendment right against self-incrimination.

Harlan Waksal, by contrast, did testify, and faced tough questioning.

“It is a tragedy,” Waksal said of the Erbitux saga.

His explanation for the scientific failures: “We’re a small company. We didn’t have the resources to do some of the quality (research) that needed to be done. … Unfortunately that’s where the errors took place.”