When installing the tools from the menu item ("Install Command Line Tools"), an error is shown (see attachment). The system log dumps the following error:

Aug 9 09:29:39 Maclet.local WindowServer[207]: [cps/setfront] Failed setting the front application to SourceTree, psn 0x0-0x86e86e, securitySessionID=0x186a7, err=-13066
Aug 9 09:29:39 Maclet.local com.apple.SecurityServer[18]: Succeeded authorizing right 'com.apple.ServiceManagement.blesshelper' by client '/usr/libexec/launchdadd' [78112] for authorization created by '/Applications/SourceTree.app' [78056] (100003,0)
Aug 9 09:29:39 Maclet.local launchdadd[78112]: FAILURE: Code <SecCode 0x7fd3529018e0 [0x7fff7682b190]> failed requirement (identifier "com.torusknot.SourceTreeNotMAS" and certificate leaf[subject.CN] = "3rd Party Mac Developer Application: Torus Knot Software Ltd") with error "The operation couldn’t be completed. (OSStatus error -67050.)"
Aug 9 09:29:39 Maclet.local launchdadd[78112]: FAILURE: Code <SecStaticCode 0x7fd352b007a0 [0x7fff7682b190]> failed requirement (identifier "com.atlassian.SourceTreePrivilegedHelper" and certificate leaf[subject.CN] = "Developer ID Application: Atlassian Pty Ltd") with error "The operation couldn’t be completed. (OSStatus error -67050.)"
Aug 9 09:29:39 Maclet.local launchdadd[78112]: FAILURE: Job com.atlassian.SourceTreePrivilegedHelper could not be installed from /Applications/SourceTree.