“ While we have very liberally construed the "in custody" requirement for purposes of federal habeas, we have never extended it to the situation where a habeas petitioner suffers no present restraint from a conviction. Since almost all States have habitual offender statutes, and many States provide as Washington does for specific enhancement of subsequent sentences on the basis of prior convictions, a contrary ruling would mean that a petitioner whose sentence has completely expired could nonetheless challenge the conviction for which it was imposed at any time on federal habeas. ”

“ In this case, the Court of Appeals held that a habeas petitioner may be "in custody" under a conviction whose sentence has fully expired at the time his petition is filed, simply because that conviction has been used to enhance the length of a current or future sentence imposed for a subsequent conviction. We think that this interpretation stretches the language "in custody" too far.
Our interpretation of the "in custody" language has not required that a prisoner be physically confined in order to challenge his § ntence on habeas corpus. ”

“ In 1976, while on parole from that sentence, he was convicted of two counts of assault and one count of aiding a prisoner to escape; in 1978, the State sentenced him to two life terms and one 10-year term on those convictions. These sentences were maximum terms under Washington's then-indeterminate sentencing scheme, with the minimum term to be set by the Board of Prison Terms and Paroles. Under Washington law, the 1958 conviction will increase by several years the mandatory minimum term which respondent will have to serve on his 1978 sentences. ”