Unbranched Riemann domains over Stein spaces

In this article, we show that if $\Pi: X\rightarrow \Omega$ is an unbranched Riemann domain with $\Omega$ Stein and $\Pi$ a locally 1-complete morphism, then $X$ is Stein. This gives in particular a positive answer to the local Steiness problem, namely if $X$ is a Stein space and, if $\Omega$ is a locally Stein open set in $X$, then $\Omega$ is Stein.